I have discovered that a highly purified biological inhibitor of epithelial cell growth rapidly and selectively induces (with a ten-fold increase) a single secreted protein from African Green monkey (BSC-1) kidney epithelial cells, and from mink (CCl4) epithelial cells. This "inhibitor-induced protein" (IIP48) (Mr = 48,000) is a glycoprotein, and its induction is inhibited by actinomycin D. To my knowledge, this is the only instance where a growth inhibitor has been shown to specifically induce a protein. In this grant period we propose to purify IIP48 and produce polyclonal and monoclonal antibodies against this protein. We shall also prepare cDNA clones to detect mRNA coding for IIP48. We shall use the antibodies and cDNA clones to analyze the mechanism by which the BSC-1 growth inhibitor regulates the production of IIP48--is the level of regulation at transcription, translation, secretion or degradation of IIP48? We shall also establish a radioimmunoassay to determine the levels of IIP48 in vivo in normal tissue at different stages of development and in cancerous tissue. With this system, I shall be able to study the mechanism of action of a nontoxic, epithelial growth inhibitor derived from a biological source (secreted by BSC-1 cells). The results are expected to help in the design of inhibitory drugs for use in the treatment of proliferative diseases of epithelial cells--particularly cancer.